The prior art is familiar with wafer handling systems. Typically, semiconductor wafers are processed through a variety of chambers and are mechanically carried between chambers by a robotic transport. These wafers are for example eight inches in diameter and have one planar surface subjected to semiconductor processes. The robotic transport supports the wafer on the other surface; so typically the first surface is upwards and the robotic transport supports the second surface underneath the wafer.
To accomplish this, the robotic transport typically utilizes a three-prong (or more) fixture that supports the wafer during transport. The prongs of the fixture are covered with a non-abrasive material, relative to the wafer, such as rubber, and are sized so as to provide sufficient surface area contact to prevent slipping during horizontal movement of the wafer through the chambers.
FIGS. 1 and 1A illustrate prior art wafer handling fixturing 8. FIG. 1 shows a side view of the fixturing 8 supporting a wafer 10. The wafer 10 has a first surface 10a and a second surface 10b. The first surface 10a is used to deposit selective semiconductor materials onto the wafer 10, such as by room temperature ion implantation. The fixturing 8 includes three representative prongs 14, supported by a base 12, that are capped with rubber pads 16 to provide good friction contact with the wafer 10 during movement 18. The pads 16 are typically between about 1/16" to 1/4" in diameter to ensure good contact with the surface 10b. FIG. 1A shows a top view of the wafer 10 and the arrangement of the pads 16 made so as to provide sufficient support. The pads 16 of FIG. 1A are illustratively shown as dotted lines.
The problem with the fixturing 8 of FIGS. 1 and 1A is that it does not survive in processes involving high temperatures, such as plasma CVD, thermal CVD, plasma vapor deposition ("PVD") and etch, and annealing. These processes can involve temperatures as high as six hundred degrees Celsius. Further, processes such as CVD and PVD are typically done in an evacuated environment; and rubber outgasses, presenting unwanted particulates and material within the deposition process. To overcome this problem, the prior art has replaced the pads 16 with a temperature-resistant material such as quartz. While this overcomes the high temperature problem, quartz and other temperature-resistant materials used in the prior art, such as brass and alumina, have low coefficients of friction with silicon. Therefore, the movements 18 must occur at low lateral accelerations so as to ensure that the wafer 10 stays on the fixturing 8 during transport. For example, typical accelerations for rubber pads can be up to about 0.5 g; while accelerations for quartz are at most 0.1 g. This reduces efficiency and production yield.
It is, accordingly, an object of the invention to provide apparatus which reduces or eliminates the afore-mentioned problems of the prior art.
A further object of the invention is to provide wafer handling fixturing that is resistant to high temperatures and that achieves high lateral acceleration, as compared to the prior art.
These and other objects will become apparent in the description which follows.